This invention relates to a cable holder, and more particularly, to a cable holder that is attached to a hole in the box plate of a distribution switchboard, a panel board and the like for holding a cable inserted in the box through the hole.
Many cable holders have been developed as means for holding a cable at a hole that is made in the box plate of a distribution switchboard and through which the cable is inserted in the board. The simplest form of these holders is a ring with an eyelet that is made of an electrically insulating, resilient material and which has an inside diameter equal or suitable to the cable diameter. The ring is attached to a hole in the box plate of a distribution board box and the cable is inserted into the box through the eyelet. The ring provided electrical insulation between the cable and the box plate without damaging the outer insulating coating of the cable, but with this ring, the cable is not always held securely. Most distribution boxes are supplied with cables of different sizes. Several cable holders are known that are adapted to various sizes of cable and which are attached to a hole in a distribution board box by, say, a locknut for securely and mechanically holding cable of any size with electrical insulation being provided between the holder and cable. One example of the holder of this type is integrally formed of a plurality of hollow cylinder elements in an array and each of the holes of the cylinder elements is axially aligned with each other. The inside diameter of each element stepwisely shortens toward the tip and the outside diameter thereof also shortens correspondingly. To insert a cable into the holder, such an integrated cylinder, the part of the cylinder elements that has an inside diameter shorter than the outside diameter of the cable to be inserted, is cut off. The cable is inserted into the cylinder element of a suitable inside diameter through the common hole of the resulting cylinder and is clamped from the outside of the cylinder element. With this type of holder, the cylinder element need not be cut off if the cable to be held has an outside diameter equal or approximate to the smallest inside diameter of the element. However, if the cable has a greater outside diameter, the need of cutting off the unnecessary part of the cylinder element increases the labor on the job site. Among the many cylinder elements that comprise the holder of this type, the cable is effectively held by only the cylinder element which is adapted to the cable diameter. Therefore, the nature of manufacture does not permit step wise arranged cylinder elements with a great axial length to be produced and the integrated cylinder only has a short length of one of the elements to effectively hold the cable. But then, the cable is easily damaged because, to get a secure grip, the cable must be placed under great stress in a small area of the element. Otherwise, not only is the cable not securely held by the holder but also, because of the shortness of the effective area of the cylinder element, the smallest gap in the holding section permits external air or moisture to enter the panel board box.